The present disclosure relates to an advance pneumatic detector (“APD”). In particular, the disclosure relates to an APD with a test feature for detecting the state of the APD.
An APD is typically comprised of both an alarm switch and a fault switch. APDs can utilize a pressure tube that contains a gas that will expand as it is heated, thus increasing the pressure in the pressure tube. An alarm switch is used to indicate overheat or fire situations. An alarm switch includes a deformable diaphragm that is at a normal state when the system is at a normal pressure. As the pressure increases in the pressure tube, the diaphragm deforms and closes an electrical circuit, indicating that there is an alarm condition in the system. A fault switch is used to indicate whether there are leaks, disconnects, or other problems in the APD. A fault switch includes a deformable diaphragm that is deformed when the system is at a normal pressure. If the pressure drops below normal, the diaphragm of the fault switch resumes its normal state and opens an electrical circuit, indicating that there is a fault condition in the system.
APDs utilizing both an alarm switch and a fault switch are used on aircraft to detect alarm and fault conditions. The pressure tubes for the alarm and fault switches can typically run anywhere from one foot long to fifty feet long, and can be placed in systems that are prone to overheating or fires. With existing APDs used in aircraft applications, such as in the engine or wing, there are no current designs that allow for in-situ testing to verify and confirm whether a switch of the APD is still functioning. Currently, to determine whether the APD is functional, the APD must be removed from the aircraft and subjected to high heat or extreme cold (e.g., liquid nitrogen bath) in order to reset the switch and/or provide indication for a low-pressure state or latent failure mode.